Enamel composition



Patented Aug. 18, 1942 ENAMEL COMPOSITION Karl Kautz, Burgettstown, Pa, assignor toCllmax Molybdenum Company, New York, N. Y., a corporation of Delaware No Drawing. Application August 10, 1940, Serial No. 352,117. In Belgium October 31, 1939 1 Claim. (Cl. 106-48) The present invention relates to new and useful improvements in. vitreous enamel compositions.

Heretofore it has long been the custom in .the

l which is more adherent to the base metal on which the enamel is applied and fused. a The invention also provides a vitreous enamel composition which requires a fewer number of coats, and

- is of a white or light color. A further object is to provide such a composition which reboils very production of vitrefied enamels to smelt into the 5 slightly, which makes possible the use of lower enamel certain substances to promote adherence temperatures in the fusion of ground coats for of the enamel to the ferrous base metal when it is enamel ware, and permits flner adjustment of applied to the surface and fired. These subthe ground coat at the mill.

stances have been cobalt oxide, either alone or in In accordance with the present invention the conjunction with nickel oxide and/or manganese adherence of the enamel coating may be prooxlde. Such a frit produces a dark blue ground moted and the opacity of light colored coats imcoat which is usually covered with other enamels proved bythe use of molybdenum salts and comcontaining opaciflers in order to leave the prodpounds in any type of enamel frit or ground coat uct with a white or light colored finish. The usumixture. The molybdenum is usually employed a1 practice is to apply two such coats, as it has in connection with antimony oxides and the been found that one heavy coat is insufficient to molybdenum compounds may be added to the completely cover the dark colored ground coat, smelt when the fritis produced or illed in with so that in the production of enamel ware three the enamel when preparing the sl p, depending distinct coats, and thus three distinct heat treat- 'upon the type of compound used d the results ments, are necessary for a finished product of the desired. When light colored coats are desired, desired quality. I v the usual smelted in cobalt, manganese, and/or It has been proposed to smelt about 1.5% nickel oxides may be omitted and the molybdemolybdenum trloxide (M003) and 7.5% antinum and antimony compounds employed, the mony oxide (SbaOa) with a typical enamel batch other ingredients'of the usual enamel frit being from which the dark-color producing substances used in substantially the same proportions. The cobalt oxide, nickel oxide, and manganese oxide first coat adheres at least as well as the cobalthave been omitted and thus to produce a light nickel-manganese frit heretofore used, and has colored ground coat which would have the necthe added advantage that due to the light color essary adherence properties. However, it was and opacity only one additional coat is required found that the results were erratic and satisfac- 3 to completely obscure the base. tory adherence was frequently notv attained, It will be understood that the foregoing gen- 7 probably due to the volatilization of the added eral description and the following detailed deoxides during the smelting of the frit. It has scription as well, are exemplary and explanatory also been proposed to electroplate the ferrous of the invention but are not restrictive thereof. base with MoO:..rH:O to promote adherence, but Referring now in detail to several illustrative this requires accurate control and added equipmethods of preparing the compounds and carryment, as well as entailing an operation whichis ing out the processes of the present invention, a foreign to the usual enamelling process. molybdenum suboxide, such as molybdenum diobjects and advantages of the invention will oxide (M002) or molybdenum blue," is milled be set forth in part hereinafter and in part will with antimony trioxide (SbaOs) infa clear frit, be obvious herefrom, or may be learned by prachas been found to produce excellent adherence tice with the invention, the same being realized when fused onthe ferrous base metal and, proband attained by means of the steps, instrumenably due to the fact that it is insoluble in the mill talities and combinations pointed-out in the apliquor, there is no crawling, tearing or peeling of pended clalm the enamel during the firing process.

The invention consists in the novel steps, proc- Successful results have been obtained throughesses, combinations and improvements herein out a considerable range of variation in the shown and described. amounts of a lower oxide of molybdenum and The present invention has for its object the antimony x e eOa) use a d the P p r provision of anew vitreous enamelcomposition 0 amounts will depend on a number of circumstances, such as, for example, the nature of the enamel, the nature of the iron surface, the thickness of the coating, and furnace conditions, and the amounts actually used in practice should be determined experimentally for each set of conditions. In general, however, it has been found that excellent adherence is attained when the proportion by weight to the frit of M: is from 0.25 to 5.0% and of SbzOa is from 0.25 to 15.0%. Experiments tend to show that the best adhere ence is generally associated with substantially two parts by weight of SbzO: to one part by weight of M002, and it is probable that the best theoretical proportion is the proportion of the atomic weights of the compounds, 1. e., 291.52 parts SbzOa to 127.75 parts M002, in accordance with the reaction theory as hereinafter set forth. Thus the use of 2.92% SbzOa, and 1.28% M00: has shown excellent results, although at times antimony blisters" are produced, but this is entirely eliminated by the addition of a slight excess of M002.

Molybdenum trioxide (M003) may likewise be used as a mill addition to a clear enamel base along with antimony trioxide (SbzOa) to produce a white or light colored ground coat with excellent adherence to the ferrous base metal. With these substances better adherence is obtained when the amount of MoOais varied between 1% and 2%, and the SbzOa between 1% and 4%, and here again the best results are associated with the proportion of substantially two parts by weight of SbzOa to one part by weight of M003, with the ideal theoretical proportion probably being the relation of the molecular weights, i. e.,. 291.52 parts SbzOa to 143.95 parts M003.

Antimony molybdate (SbsOa-MOOs) has proved to be an excellent adherence producing agent, and it may be milled with a clear enamel base in amounts varying from 3% to 4% in order to produce the best results. Its use imparts a brownish-yellow color to the enamel so that M002 and/or M00: used with 81320:; are to be preferred when a white enamel is desired.

Excellent adherence may be obtained by the use of the barium antimony molybdates, and these are advantageous for the reason that the antimony and molybdenum oxides are thus used in a very insoluble form. 2BaO-SbaOs-M0Oa produces a white enamel, while a yellow enamel may be obtained by the use of BaO-SbzOa-MoOa, and a yellow-brown color by use of BaO SbzOs 2Mo0a Calcium antimony molybdate (ZCaO-SbaOrMOOa) will also produce a yellow-brown color in the enamel.

The use of molybdenum compounds is not limited to their addition to aprepared frit in the milling operation where the final slip is prepared. They may alsobe used as an initial ingredient in the smelting of the frit. Thus complex salts and compounds of molybdenum which yield a suboxide of molybdenum on being heated to relatively high temperatures such as are em-- ployed for enamelling, such as the salts of ammonia and the amines may be added directly to the smelt, and the suboxides of molybdenum will be formed during the smelting operation and be an ingredient of the finished enamel.

The use of such complex compounds of molybdenum either as mill additions or as enamel ingredients has been found to have the additional advantage that when heat is applied and a subent in the slip in very finely divided form, and thus the necessity for extremely careful grinding is avoided as when the suboxides are milled in with the enamel. Thus the present invention has been found to yield excellent results when antimony oxide is smelted into the enamel batch, and ammonium molybdate added during the milling operation.

While the invention has been disclosed in certain preferred embodiments using a suboxide or trioxide of molybdenum together with antimony trloxide, or using antimony molybdate alone, as mill additions to enamel, or using certain compounds of molybdenum in the preparation. of enamels, and certainother compounds have been suggested, it will be understood that said embodiments are merely examples of the invention, and are not to be taken as limiting or defining the larger application of the invention as a whole. Thus, results withinthe scope of the present invention may be obtained by the use of any of those substances separately, as well as by the use of other antimony and molybdenum compounds either separately or in combination. For

oxide of molybdenum produced, it will be pres- 7 instance, sodium antimoniate and molybdenum dioxide, calcium antimoniate and calcium molybdate, or antimony oxide and calcium molybdate may be used as mill additions to the ground coat enamel. Complex compound such as molybdenum blue, which may be represented by the formula :cMoOz-yMoOa-zHaO produce excellent opacity and adherence.

The alkali, alkaline earth, ammonium, amine, zinc, leadand other metallic salts of the molybdenum acids may be used as the source of molybdenum, and likewise the antimoniates of the alkali metals, alkaline earth metals, ammonium, zinc, lead and cadmium, as may be the complex antimono and arseno-molybdates of calcium, zinc, lead and cadmium, and the like.

Experiments have tended to show that the principal factor which influences the adhesion of enamels to iron is the presence of oxygencarrying agents in enamel. Cobalt and nickel compounds as heretofore used in enamel batches are understood to absorb oxygen from the air and give it up to the iron base. It is believed that molybdenum and antimony compounds used in accordance with the present invention also do this. Thus, when a light-colored ground coat, containing milled-in Sb20a and M00: is heated in contact with iron, the following reactions may occur:

In the early stages of firing, before the enamel fuses, MoO: absorbs oxygen to form M003, which from the furnace atmosphere. This reaction is probably cyclical, continuing throughout the firing period, and the oxidation of the iron base takes place continuously under the fused glassy coating. It has been observed that adherencev is adversely affected by the use of opaciflers in the ground coat, and that successful ground coats must have good fluidity, and these facts are probably due to the necessity of having atmospheric oxygen easily available for theabove reactions occurring at the surface of the iron.

It will be understood that the foregoing discussion of reactions is only a possible and reasonable explanation of the observed results of the present invention, is empirical only, and is not to be understood as limiting the scope or application of the invention.

Frit

clay 70 Borax 7.5v

Calcium molybdate 12.5 Water 550 In addition to the presence of oxygen-carrying agents in the enamel, and good fluidity of the, milled material when it is placed upon the metal surface to be fired, it has been found that a third factor essentl for the adherence of an enamel ground coat is a surface free from grease, oil or dirt. The degree of pickling or etching ofthe surface which should be affected depends upon the oxidizing conditions which will be encountered in the firing process. When a laboratory furnace is to be used having a slow comeback,

deep etching is necessary'to bring about maximum adherence. In industrial furnaces, both box and continuous, where severe oxidizing conditions and rapid heat transference occur, lighter pickling is sufficient for good adherence.

When the present invention is practiced by using the molybdenum compounds as mill additions, a number of different enamel batches may be used to produce the frit. In general, any,

cobalt enamel batch with the coloring oxides omitted may be used, and different batches may be chosen in order to secure 'ground coats with different heats of fusion; Thus a typical smelter batch to produce ground coats maturing at 1580 to 1600 F. is:

Per cent Borax 35.5 Feldspar 26.0 Quartz 20.5 Soda ash 6.6 Soda niter- 5.3 Fluorite v 6.1

and such a frlt may be used as the basisof a mill batch addition ofmolybdenum, as follows:

Grams Frit 1000 Clay Borax 5 Antimony trioxide; v 12.5- Calcium molybdate 12.5 Water--- T 550 or 7.5 g. molybdenum trl xide may be substituted for the calcium molybd A small amount of antimony oxide may be smelted-in, in which case the batch is:

Per cent Borax 34.4 Feldspan 25.0 Quartz 19.8 Soda ash 6.4 Soda niter 5.1 Fluorite 5.8 Antimony trioxide 3.5

' instance, are wet milled'together and then dried.

To this melted batch, the other ingredients may be added in the following proportion:

and 7.5 parts '0: (minute. may be substituted for the calcium molybdate with good results.

A softer ground coat, which may be used at 1500 F. or lower is: 1

. Per cent Borax 47.4 Feldspar 17.3 Quartz 16.6 Soda ash 4.9 Soda niter 2.7

' Barium carbonate 6.1 Fluorite 4.8

This is then smelted, milled, and the following milled in:

Frit 1,000 Clay 70 Borax 5 Antimony trioxide 10 Calcium molybdate 15 Water 550 This batch, also, may contain smelted-in antimony trioxide, and the firing range will be th'e same:

(15 parts lead molybdate' may be substituted for the ammonium molybdate.)

In general the frits are milled in the usual I manner to about 8 grams on 200 mesh for a gram sample; a typical mill batch being Frit--- 1.000 .Vallendar clay 70 Borax 5 Water 550 and the adherence promoting compounds are added and milled-in in the amounts heretofore discussed.

These enamel batches or others may likewise be used' when the molybdenum compoimd is smelted directly into the frit.

' Although it is not essential to the success of the process, it has been found that the gloss and texture as well as the uniformity of the enamel is promoted when the desired amounts of adherence promoting compounds, 81020: and M001, for

before addition to the mill batch for grinding with 100.0 70 the frit. I

Other specific examples of enamels illustrative of the present invention are the following:

WHITEYGSOUND Cour A! 1550' ll.

Smelter batch Mill batches Per cent Frit 1,000 Borax 28.75 Clay '60 Feldspar 25.20 (NH4):MoO4 "1.5 Quartz 19.90 Water 500 Cryolite 12.65 or Soda ash. 1.60 Writ... 1,000 Soda antimoni- Clay 60 ate 5.81 :PbMooi 12.5 Fluorite 3.53 Water..-.. 500 Soda niter 2.56 x

ONE-COAT WHITE ENAMEL n 1550 F.

Smelter batch Mill batches Per cent Frit 1,000 Borax 1 27.6 Clay 6o Feldspar 424.2 (NH4MM004 6 Quartz 19.1 Water 450 Cryolite 12.1 or Sodium antimo- Frit 1,000 niate 11.2 Clay 60 Soda niter 2.4 Sodium nitrite 3 Fluorite 3.4' PbMo04 20 Water 450 While .the invention has been described with considerable particularity as applied to ground coats. and the preferred composition for carryin: it out have been disclosed, it will be appreciated by those skilled in the art that the invention is of wider application; is applicable to sheet steel cover coat enamels, hollow-ware enamels and cast iron enamels as well, and that other compositions than those described may'be used. Reference is therefore to be had to the appended claim for a definition of the-limits or the invention.

What I claim is: l

The process of enamelling iron metal ware. comprising milling the i'rit with an oxide of molybdenum and with an oxide of antimony, the amount of the molybdenum oxide with relation to the Irit being from .25 to 5.% by weight and the amount of the oxide of antimony being twice the amount of the molybdenum oxide, and applying L 'molybdate to give an enamel 01' good adherence to iron.

KARL KAU'IZ. 

